1. Field of the Invention
The present invention relates to a toner for use in an image-forming method which utilizes electrophotographic technology, electrostatic recording technology or toner jet recording technology.
2. Description of the Related Art
How to implement energy savings in electrophotographic equipment has become a major technical concern in recent years. One solution has been to cut down markedly on the quantity of heat applied to the fixing apparatus. This has led to an increased need in toners for “low-temperature fixability” which enables fixing to occur at a lower energy.
One method that is known to be effective for enabling fixing to occur at lower temperatures is to make the binder resin sharper melting. It is in this connection that toners which use crystalline polyester resins have been proposed. Because crystalline polyesters, owing to the arrangement of the molecular chain, do not exhibit a distinct glass transition and do not readily soften up to the crystal melting point, they are being investigated as materials which are capable of achieving both heat-resistant storage stability and low-temperature fixability.
However, when a crystalline polyester is used alone as the toner binding resin, the toner has a sharp melting property, but lacks elasticity at elevated temperatures, as a result of which hot offset and a decrease in the degree of gloss due to penetration into the paper may arise and the fixing temperature range may narrow. Hence, in continuous image formation under a low-temperature environment in a printer, offset and uneven gloss have tended to arise, preventing stable images from being obtained.
Therefore, toners have been proposed in which a smaller amount of crystalline polyester is added and crystalline polyester and non-crystalline polyester are used in admixture.
Japanese Patent Application Laid-open No. 2004-191927 attempts to enhance the fixing latitude by controlling the storage elastic modulus and loss elastic modulus at the melting point+20° C. in a capsule-type toner containing a crystalline polyester and a non-crystalline polyester.
In cases where a small amount of crystalline polyester is added to non-crystalline polyester, this changes the viscosity of the non-crystalline polyester, enabling the viscosity at high temperatures to be adjusted and thus making it possible to suppress hot offset. However, in such cases, the sharp melt properties of the crystalline polyester are not fully exhibited, making it impossible to fully manifest the effects on the low-temperature fixability.
To resolve such problems, toners have been proposed which make use of a binder resin composed of a crystalline polyester and a non-crystalline polyester that are block copolymerized.
Japanese Patent Application Laid-open No. 2007-114635 shows that, by using a block copolymer obtained by the esterification of crystalline polyester blocks and non-crystalline polyester blocks, fixing by low-temperature heating is possible.
Japanese Patent Application Laid-open No. 2008-052192 shows that a toner of improved heat-resistant storage stability and hot offset resistance is achieved with a urea-modified polyester obtained by using an amino crosslinking agent to modify crystalline polyester segments and amorphous polyester segments.
Japanese Patent Application Laid-open No. 2010-168529 discloses a toner obtained by dispersing, in carbon dioxide in a liquid or supercritical state, an organic solvent solution of a resin composed of crystalline segments which contain as an essential ingredient an aliphatic polyester (i.e., crystalline polyester) and non-crystalline segments so as to form resin particles, then removing the organic solvent and the carbon dioxide.
However, even in cases where toners containing such block polymers are used, with regard to the low-temperature fixability, particularly when the wax dispersibility within the toner is inadequate, there are times where cold offset arises and sufficient effects cannot be obtained. Also, in cases where the crystalline polyester is insufficiently crystallized, the heat-resistant storage stability may be inadequate or, depending on the particular wax used, a decrease in the heat-resistant storage stability may arise on account of wax bleedout or a decline in crystallinity owing to compatible mixture of the crystalline polyester and the wax. In particular, when the toner has stood for a long time in an environment subjected to repeated temperature cycling, degradation in the heat-resistant storage stability has tended to arise. Hence, there exists a desire for an even more improved toner.